The present invention relates generally to hermetic compressors of the type having a hermetic housing, wherein a hermetic terminal is provided for carrying electric current into the housing and, more particularly, to such a terminal that provides an electrically insulating oversurface distance between the current-conducting pins and the metallic body member of the hermetic terminal.
Terminal assemblies for hermetic compressors are well-known in the art and generally comprise a cup-shaped metallic body member having a plurality of metallic conductor pins extending therethrough. The pins are generally glass-sealed to the insulator body to prevent leakage to or from the atmosphere.
A problem associated with prior art electrical terminals for hermetic compressors is that, during compressor operation, a process known as electrophoresis may occur, whereby metallic particles present within the system migrate toward and deposit upon the hermetic terminal conducting pins and the surface of the glass seal insulator. Also, other phenomena may result in the presence of carbonaceous contaminants within the housing. These particles and contaminants can accumulate to the extent that an electrically conductive path is formed between a pin and the metallic body member, i.e., a ground fault, or between respective pins, i.e., a short circuit, thereby resulting in terminal failure.
One method for preventing or minimizing the occurrence of the aforementioned failure mode of the hermetic terminal is to provide an electrically insulating cap around the terminal to increase the pin-to-ground oversurface distance. In U.S. Pat. No. 2,458,748, an electric terminal having a hermetic seal includes an insulating collar disposed over a glass seal between a terminal pin and a metal wall through which the pin extends, thereby providing an extended leakage path for current therebetween. Although such an insulating collar increases the oversurface distance between the terminal pin and the metal wall, the collar is still susceptible to having contaminants deposited thereon, thereby providing a leakage path.
It is desired to provide a hermetic terminal that is effective in minimizing terminal failure due to ground faults or short circuits caused by the build up of electrically conductive contaminants within the system.